Here is a CBS News report on how the affair between Gen. David Petraeus and his biographer, Paula Broadwell, was discovered. Apparently, Broadwell sent jealous emails to another woman – a family friend of Petraeus and his wife – because she thought the woman was getting too close to Petraeus. The emails reportedly said things like, “stay away from my guy.” The woman who received the emails contacted the FBI, and they began an investigation which traced the emails back to Broadwell and uncovered the affair with Petraeus.